Question: Solve for $z$ : $13 = -9 + z$
Add $9$ to both sides: $ \begin{eqnarray} \\ \hphantom{13 {+ 9}} &\hphantom{=}& \hphantom{z} \\ 13 &=& -9 + z \\ \\ {+9} && {+9} \\ \end{eqnarray} $ $ \begin{eqnarray} \\ 13 {+ 9} &=& z \\ \end{eqnarray} $ Simplify. $ z = 22$